Leave the definition of models to the bootstrapper

Depends on strongloop/loopback-boot#11.

/to @ritch 
> > implement Model.remoteMethod as a wrapper around loopback.remoteMethod

> This shouldn't be our solution for "I need a reference to something not available from Todo or Base".

I agree. Although as the example with `Model.remoteMethod` shows us, the loopback class is to greedy and doing too much; we may discover other methods that should belong to different classes.